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stumbleman
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Simple average problem, but not sure what's wrong? 12 Oct 2005, 17:52
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Hi all,

new to the forum - just going through my Kaplan GRE/GMAT Math Review book, and I was doing the exercises after the "Averages" review in Arithmetic. Came across this problem:

What is the value of x if the average of -4,0,6,x is 8?

The book says the answer is 30, but I keep getting 22. Am I doing something wrong? Kaplan helpfully gives no explanation for the initial exercises, so I have no idea what I'm dong wrong. Any help would be appreciated.

thanks!

Mike (A.K.A. Haven't done math in 10 years)



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Simple average problem, but not sure what's wrong? 12 Oct 2005, 18:01
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Guess you getting some arithmatic worng (as most of us do at times :) )

avg of -4,0,6,x is 8
or

(-4 + 0 + 6 + x) / 4 = 8
or
(2 + x) / 4 = 8
or
2 + x = 32 or
x = 32 - 2 = 30
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stumbleman
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Simple average problem, but not sure what's wrong? 13 Oct 2005, 16:29
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Thanks! Quite straightforward when solving with Algebra, but the method the book describes (one new to me) is to compare the number to 8. i.e.:

-2 is 6 LESS than 8
0 is 8 LESS than 8
4 is 4 LESS than 8

Therefore:

10 + 8 + 4 = 22

this is 22 LESS than the average, therefore x equals 8 + 22.

Convoluted, I know. I much prefer the algebraic method to solve. Kaplan kills me.

mike
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sudhagar
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Simple average problem, but not sure what's wrong? 13 Oct 2005, 16:46
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stumbleman: I am not sure which version of Kaplan do you have. But I believe they have the Math reference section towards last part of the book (after Data Sufficiency).

In that section they have about 100 key items and you should be able to pick these things from there.



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